Java – @Pattern , JSR303 bean validation : regex check max 5 words and not blank

bean-validationjavaregexspring-mvc

I use JSR303 bean validation annotations in my spring-mvc managed bean to validate text input.
I need to check

if a string contains max 5 words (Here a word is an alphabetic or alphanumeric string)
and this string can't be blank (one space)

I try with this : ( just to match 5 words)

@Pattern(message="max 5 words please" , regexp="^[a-zA-Z+#\-.0-9]{1,5}(\s[a-zA-Z+#\-.0-9]{1,5}){0,4}$")
String keywords;

but my Eclipse IDE says :
Invalid escape sequence (valid ones are \b \t \n \f \r \" \' \ )

Best Answer

You could try this shorter version if you want.

regexp="^(\\b[a-zA-Z\\d+#.-]+\\b(?:\\s+|$)){0,5}$")

Should work.

Btw in your regex you say :

Match one to five chars (word of max 5 chars?), (followed by space, followed by zero to four chars. ) zero or four times. Is this what you want? :)

Related Solutions

Firewall – WAF vs Firewall

A "regular" firewall typically only looks at layers 3 and 4 of the OSI model. For instance, to allow TCP port 80, allow UDP port 53 from only specific IP addresses, or deny TCP port 25.

For HTTP requests, once the "allow TCP port 80" hurdle is cleared, the firewall is uninterested in what's passed via that connection.

A Web Application Firewall works almost exclusively at layer 7, dealing with security in terms of the content of HTTP requests.

Mainly, they're looking to prevent requests that are outside what should be expected for your web application, using rules applied to incoming HTTP requests to prevent attacks like cross-site scripting, SQL injection, directory traversal, or brute-force authentication attempts. Essentially, their whole purpose is shielding the web server from the kinds of manipulated and malicious requests that attackers might use to compromise your web application.

Regex – How to check if a line is blank using regex

The pattern you want is something like this in multiline mode:

^\s*$

Explanation:

^ is the beginning of string anchor.
$ is the end of string anchor.
\s is the whitespace character class.
* is zero-or-more repetition of.

In multiline mode, ^ and $ also match the beginning and end of the line.

References:

regular-expressions.info/Anchors, Character Classes, and Repetition.

A non-regex alternative:

You can also check if a given string line is "blank" (i.e. containing only whitespaces) by trim()-ing it, then checking if the resulting string isEmpty().

In Java, this would be something like this:

if (line.trim().isEmpty()) {
    // line is "blank"
}

The regex solution can also be simplified without anchors (because of how matches is defined in Java) as follows:

if (line.matches("\\s*")) {
    // line is "blank"
}

API references

String String.trim()
- Returns a copy of the string, with leading and trailing whitespace omitted.
boolean String.isEmpty()
- Returns true if, and only if, length() is 0.
boolean String.matches(String regex)
- Tells whether or not this (entire) string matches the given regular expression.